Whole-orchard recycling improves air quality, soil characteristics

The Almond Board of California (ABC) last December embarked on a journey to accelerate research on certain pressing almond sustainability issues, including water management and air quality.

The Almond Board of California (ABC) last December embarked on a journey to accelerate research on certain pressing almond sustainability issues, including water management and air quality.

At the same time, San Joaquin County farm advisor Brent Holtz presented his research on the feasibility of ripping up, grinding, and incorporating entire almond orchards back into the soil where the trees once grew.

Supported by ABC’s Accelerated Innovation Management (AIM) program, Holtz’s ongoing research continues to look at the effects of incorporating the biomass of an entire orchard on soil characteristics, plus the growth and productivity of second-generation almond trees planted in the orchard.

According to Holtz, his research results suggest that the trees will do just as well or better in the presence of additional organic matter which increases water infiltration and water-holding capacity. In addition, as the woody material breaks down over time, it releases nutrients, including up to 1,500 pounds of potassium and 800 pounds of nitrogen per acre.

If these results continue in ongoing studies, growers will potentially save on water and crop inputs, including fertilizer and soil amendments.

Equipment demonstration

Five pieces of equipment rumbled through an old almond orchard in Manteca recently as Holtz demonstrated a new way to perform whole-orchard recycling. An excavator uprooted trees, a front-end loader transported the trees to a horizontal chipper, and a spreader and rototiller then spread the chips on the ground for incorporation into the soil.

In his original studies, the researcher used an IronWolf, a 50,000-pound rototiller that ripped whole trees out of the ground, shredded them, and incorporated the shreds into the soil.

According to Holtz, the five pieces of equipment outperformed the IronWolf. The IronWolf costs about $1,500 an acre to operate, and recycles trees at the rate of two acres a day.

The five different machines together cost about $1,000 per acre to operate, and cover 15 to 20 acres a day. Moreover, the horizontal wood chipper grinds the trees more evenly and into finer particles than the IronWolf, which left some sizeable chunks behind.

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This brings the whole-orchard recycling option closer to economic feasibility for growers facing the process of replacing old orchards.

The demonstration was held at Tallerico Farms. The chipper, spreader, and rototiller equipment was operated by Randy Fondse of G&F Agricultural Services in Ripon.

Soil, tree effects

In addition to researching a practical equipment option, Holtz’s work over eight years has looked at the effects of the woody biomass on soil characteristics and the growth of second-generation trees planted to this soil. As the wood breaks down, it not only returns nutrients to the soil, the increased organic matter results in carbon sequestration, important for moderating the release of greenhouse gases into the atmosphere.

Favorable option

With burning no longer an option due to air quality concerns and cogeneration plants shutting down, incorporating the whole orchard appears to be a viable alternative for recycling almond orchards. It not only improves air and soil quality, but also appears to make economic sense for growers.

Holtz reports cumulative yield increases of 200 pounds of almonds per acre compared to trees that were grown in soil where trees were burned before incorporation. This would pay for the cost of processing and incorporating the trees.

The results of this work are promising. At the moment, incorporating almond orchards is the next-best alternative to cogeneration if that is not an option, especially for growers who have sandier soils, in which case the large amount of biomass providing better water-holding capacity is especially valuable.

However, I would caution that more work needs to be done. So far, we really have only one set of trial data so I would encourage growers to conduct simple experiments by incorporating whole trees in one part of an orchard to show comparisons.

Meanwhile, the ABC, with a generous grant through USDA’s Specialty Crop Block Grant Program, along with Dr. Holtz and his colleagues, will continue to evaluate the short- and long-term impact of whole-orchard recycling on the health and growth of second-generation trees planted in the orchard, soil health, the orchard’s carbon footprint and nitrogen dynamics, plus yield response to periods of reduced irrigation.

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